public class UsePostorderAndInorderCreateTree {

    static class TreeNode {
        public int val;
        public TreeNode left;//存储左孩子的引用
        public TreeNode right;//存储右孩子的引用

        public TreeNode(int val) {
            this.val = val;
        }
    }

    public int postIndex;

    public TreeNode buildTree(int[] inorder, int[] postorder){
        postIndex = postorder.length-1;
        return buildTreeChild(inorder,postorder,0,inorder.length-1);
    }

    public TreeNode buildTreeChild(int[] inorder ,int[] postorder,int inbegin,int inend){
        //这种情况下 表明 当前root 没有子树了
        if (inbegin>inend){
            return null;
        }

        TreeNode root = new TreeNode(postorder[postIndex]);
        int rootIndex = findVal(inorder,inbegin,inend,postorder[postIndex]);
        postIndex--;

        root.right = buildTreeChild(inorder, postorder, rootIndex+1, inend);

        root.left = buildTreeChild(inorder, postorder, inbegin, rootIndex-1);

        return root;

    }

    private int findVal(int[] inorder, int inbegin, int inend, int val){
        for (int i = inbegin; i <= inend; i++) {
            if (inorder[i] == val){
                return i;
            }
        }
        return -1;
    }
}
